Cylinder head for piston refrigeration compressor, compression unit including such cylinder head, and piston refrigeration compressor including said compression unit

ABSTRACT

A cylinder head for a piston refrigeration compressor that includes at least a first part defining a cooling-gas suction chamber and at least a second part defining a cooling-gas discharge chamber, the first and second parts being distinct from each other, and the suction and discharge chambers each being intended to be brought into communication with a compression chamber provided in the compressor. The cylinder head includes thermal insulation means provided between the first and second parts, the thermal insulation means including an insulation chamber defined by the first and second parts.

The present invention concerns a cylinder head for piston refrigeration compressor, a compression unit including said cylinder head, and a piston refrigeration compressor including said compression unit.

A cylinder head for piston refrigeration unit comprises, in a known manner, a cooling-gas suction chamber and a cooling-gas discharge chamber, the suction and discharge chambers each being designed to be brought into communication with a compression chamber provided in the compressor.

One drawback of this type of cylinder head lies in the fact that the cooling gas to be compressed that is suctioned in the suction chamber is heated by the compressed cooling gas discharged into the discharge chamber.

This heating of the cooling gas to be compressed causes an increase in the temperature and enthalpy of that gas, and a decrease in its density. This decrease of the density of the cooling gas to be compressed causes a decrease of the mass of gas compressed by the compressor, and therefore reduced heat energy, for a same volume of swept gas. Due to the intrinsic properties of the cooling gas (the slope of the isentropics in the dry steam field evolves with superheating), the compression work by unit of mass increases following said superheating of the compressed gas, and because of this, the energy yield of the compressor is reduced. This results in a decrease in the compressor's performance.

Another drawback concerning piston compressors, in particular those that must operate at high discharge pressures, is that it is necessary to realize rigid cylinder heads so that the pressure exerted by the cylinder head on the joints situated between them and the valve plate, and between the valve plate and the cylinder block, respectively, is sufficient to avoid leaks of the cooling gas. In order to realize rigid cylinder heads for applications with high pressures, it is necessary to have parts with great inertia, therefore massive and heavy.

Furthermore, the increased rigidity of the cylinder head translates to an increase of the heat conduction surfaces, and therefore increased heating of the cooling gas.

The present invention aims to resolve these drawbacks.

The technical problem at the base of the invention therefore consists of providing a cylinder head for piston refrigeration compressor that has a simple and compact structure, and that makes it possible to avoid heating of the cooling gas to be compressed by the compressed cooling gas.

To that end, the present invention concerns a cylinder head for piston refrigeration compressor, comprising at least a first part defining a cooling-gas suction chamber and at least a second part defining a cooling-gas discharge chamber, the first and second parts being distinct from each other, the suction and discharge chambers each being designed to be brought into communication with a compression chamber provided in the compressor, wherein it comprises thermal insulation means provided between the first and second parts, the thermal isolation means including an isolation chamber defined by the first and second parts, and wherein one of the first and second parts comprises a tubular portion and wherein the other part comprises a through passage, the tubular portion being arranged to be inserted into the through passage so as to define the isolation chamber between the outer wall of the tubular portion and the inner wall of the through passage.

The realization of the cylinder head from two distinct parts and the arrangement of thermal isolation means between these two parts makes it possible to thermally isolate the suction and discharge chambers, and therefore to avoid a thermal transfer between them. It results from this that the cooling gas to be compressed cannot be heated by the compressed cooling gas.

Because of this, the performance of a compressor equipped with a cylinder head according to the invention is improved.

Making the cylinder head from two distinct parts makes it possible to decrease the machining time of the cylinder head, use different materials for the two parts, and also obtain precise geometries of the isolation chamber.

Making the cylinder head using two distinct parts also makes it possible to realize a cylinder head having a low mass. The successive assembly of the first part defining the suction chamber and the second part defining the discharge chamber makes it possible to apply sufficient pressure on the surfaces of the joints separating the low pressure zone from the high pressure zone in order to avoid leaks of refrigerating gas.

Advantageously, the isolation chamber includes a volume of air at atmospheric pressure, a volume of cooling gas, such as CO2, at low or high pressure, a thermally isolating material, or a combination of these different elements. When this isolation chamber is situated in a cooling-gas flow zone, the gas speed inside it is practically zero. In that case, the isolation chamber has a thermal resistance made up of a wall of the first part, a space for gas at practically zero speed, and a wall of the second part. The presence of cooling gas at practically zero speed between the walls of the first and second parts limits the convection effect between these two walls, and therefore reduces the heat transfer between the first and second parts. The presence of this cooling-gas pressurized isolation chamber therefore makes it possible to avoid heating of the cooling gas to be compressed.

According to another embodiment of the invention, the tubular portion has a groove extending over its entire periphery.

Preferably, the part comprising the through passage has a return turned toward the inside of the through passage, the return being arranged to cooperate with the tubular portion.

Advantageously, the return extends over the entire circumference of the through passage.

According to one embedment of the invention, a gasket is situated between the return and the tubular portion.

Advantageously, the return and the tubular portion define a groove designed to be filled with cooling gas under operating conditions of the piston refrigerating compressor.

Preferably, the isolation chamber is essentially annular.

The present invention also concerns a compression unit for piston refrigeration compressor, comprising a valve plate and a cylinder block, wherein it comprises a cylinder head according to the invention.

The present invention also concerns a piston refrigeration compressor comprising a compression unit according to the invention.

In any event, the invention will be well understood using the description which follows, done in reference to the appended diagrammatic drawing illustrating, as a non-limiting example, one embodiment of a compression unit for piston refrigeration compressor according to the invention.

FIGS. 1 and 2 are two longitudinal cross-sections.

FIG. 3 is a cross-sectional view along line III-Ill of FIG. 1.

FIG. 4 is a detailed view of FIG. 1, enlarged.

FIG. 5 is a cross-sectional view along line IV-IV of FIG. 2.

FIGS. 1 to 5 illustrate a compression unit 2 for piston refrigeration compressor.

The compression unit 2 comprises a cylinder head 3, a valve plate 4 and a cylinder block 5, only the cylinder 5 of which is shown in the figures.

The cylinder head 3 comprises a first essentially cylindrical part 6. The first part 6 is fastened on the valve plate 4. The first part 6 comprises two radial cooling gas inlets 7, 7′ and defines an essentially annular cooling-gas suction chamber 8 into which the radial inlets 7 lead.

The first part 6 comprises an axial through passage 9, the axial passage 9 being defined by a cylindrical surface.

The first part 6 has, at its face turned toward the valve plate 4, a radial return 11 turned toward the inside of the through passage 9, the return 11 extending over the entire circumference of the through passage 9.

The cylinder head 3 comprises a second part 12 axially fastened on the first part 6 by screws 13. The assembly by screwing of the second part 12 on the first part 6 makes it possible to have a degree of freedom of angular orientation between the first and second parts during their assembly.

The second part 12 defines an axial cooling-gas discharge chamber 14 and comprises a cooling-gas discharge outlet 15 radially opening into the discharge chamber 14.

The second part 12 comprises a first portion in flange form 16 including the discharge outlet 15 and a second tubular portion 17 inserted into the through passage 9.

As shown more particularly in FIG. 4, the tubular portion 17 comprises, at its free end, a shoulder 18 forming an axial stop cooperating with the return 11. An annular gasket 19 is situated between the return 11 and the tubular portion 17.

The second tubular portion 17 has an annular groove 21 provided on its outer surface.

The outer wall of the tubular portion 17 and the inner wall of the through passage 9 define an annular thermal isolation chamber 22.

The isolation chamber 22 includes a volume of air at atmospheric pressure.

As shown more particularly in FIG. 4, the outer wall of the tubular portion 17 and the inner wall of the through passage 9 define an annular groove 23 designed to be filled with cooling gas during the operation of the compressor via a flow channel 24 connected to an annular chamber 25 defined by the valve plate 4. This flow channel 24 is realized by a play between the free end of the tubular portion 17 and an adapted gasket 32 situated between the valve plate 4 and the cylinder head 3.

The presence of the annular groove 23 and of the gasket 19 makes it possible to thermally isolate the return 11 and the tubular portion 17.

The suction 8 and discharge 14 chambers are each designed to be brought into communication with a compression chamber 26 defined by the cylinder 5 via the valve plate 4.

The valve plate 4 comprises a suction passage 27 leading into the suction chamber 8 and the compression chamber 26, respectively, and an annular valve 28 situated on the lower face of the valve plate 4 and arranged to control the flow of cooling gas through the suction passage 27. The annular valve 28 is kept in closed position by a flexible element 34.

The valve plate 4 also comprises a discharge passage 29 leading into the discharge chamber 14 and the compression chamber 26, respectively, and an annular valve 31 situated on the upper face of the valve plate 4 and arranged to control the flow of cooling gas through the discharge passage 29. The annular valve 31 is kept in the closed position by a flexible element 35.

A second adapted gasket 33 is situated between the valve plate 4 and the cylinder block.

It must be noted that the assembly by screwing of the first and second parts makes it possible to precisely control the pressure applied on the gaskets 19, 32, 33.

The operation of the compression unit 2 will now be described.

When the piston (not shown in the figures) of the cylinder block moves in the cylinder 5 in the direction of arrow A, a suction force is generated in the cylinder 5. This suction force causes a suction of the cooling gas in the suction chamber 8 via cooling gas inlets 7. The cooling gas is then suctioned in the compression chamber 26 via the suction passage 27 defined by the valve plate 4. A ring 36 inserted into the suction chamber 8 advantageously makes it possible to guide the cooling gas toward the suction passage 27, and therefore to limit the turbulence of the flow. Moreover, this ring 36 reduces the exchange surface seen by the cooling gas. Preferably, the ring 36 is made in a material limiting heat conduction, such as polymers or a foam.

When the piston moves in the cylinder 5 in the direction of arrow B, a discharge force is generated in the cylinder 5. Because of this, the compressed and heated cooling gas is discharged into the discharge chamber 14 of the cylinder head 3 via the discharge passage 29 of the valve plate 4.

The cooling gas flowing in the suction chamber 8 cannot be heated by the compressed and heated cooling gas flowing in the discharge chamber 14 due to the presence of the isolation chamber 22, the gasket 19 and the annular groove 23, which prevent a heat transfer between the first and second pieces 6, 12.

According to one embodiment of the invention, the cooling gas flowing in the compression unit is CO₂.

According to other embodiments of the invention, the isolation chamber 22 could include a volume of CO₂ at low or high pressure, or a thermally isolating material.

It goes without saying that the invention is not limited solely to the embodiment of this cylinder head described above as an example; on the contrary, it encompasses all alternative embodiments. In particular, the suction and discharge circuit of the cooling gas in the cylinder head could thus be reversed. The second part 12 could therefore define a cooling-gas suction chamber 14 connected to a suction inlet 15, and the first part 6 could define a cooling gas discharge chamber 8 connected to two discharge outlets 7. Moreover, the axial passage 9 could be defined by a non-cylindrical surface, and the compression unit 2 could comprise a single cooling gas inlet 7. 

1. A cylinder head for piston refrigeration compressor, comprising at least a first part defining a cooling-gas suction chamber and at least a second part defining a cooling-gas discharge chamber, the first and second parts being distinct from each other, the suction and discharge chambers each being designed to be brought into communication with a compression chamber provided in the compressor, comprising thermal isolation means situated between the first and second parts, the thermal isolation means including an isolation chamber defined by the first and second parts wherein one of the first and second parts comprises a tubular portion and wherein the other part comprises a through passage, the tubular portion being arranged to be inserted into the through passage so as to define the isolation chamber between the outer wall of the tubular portion and the inner wall of the through passage.
 2. The cylinder head of claim 1, wherein the isolation chamber includes a volume of air at atmospheric pressure, a volume of cooling gas, such as CO₂, at low or high pressure, a thermally isolating material, or a combination of these different elements.
 3. The cylinder head of claim 1, wherein the tubular portion has a groove extending over its entire periphery.
 4. The cylinder head of claim 1, wherein the part comprising the through passage has a return turned toward the inside of the through passage, the return being arranged to cooperate with the tubular portion.
 5. The cylinder head of claim 4, wherein the return extends over the entire circumference of the through passage.
 6. The cylinder head of claim 4, wherein a gasket is situated between the return and the tubular portion.
 7. The cylinder head of claim 4, wherein the return and the tubular portion define a groove designed to be filled with cooling gas under operating conditions of the piston refrigeration compressor.
 8. The cylinder head of claim 1, wherein the isolation chamber is essentially annular.
 9. A compression unit for piston refrigeration compressor, comprising a valve plate and a cylinder block, wherein it comprises a cylinder head according to claim
 1. 10. A piston refrigeration compressor comprising a compression unit according to claim
 9. 